Living bodies show allergic reaction not only to foreign substances of the outer world, but also to their own components, resulting in the development of autoimmune disorders. Such autoimmune disorders are systemic diseases which are divided into organ-specific autoimmune diseases such as pernicious anemia, Goodpasture's syndrome, myasthenia gravis, insulin-resistant diabetes, atrophic nephritis, multiple sclerosis and the like, and organ-nonspecific autoimmune diseases such as rheumatoid arthritis, systemic lupus erythematosus, polymyositis and the like. Various autoantibodies and autoantigen-reactive lymphocytes are present in such autoimmune disease, and it has been an important issue how they are actually related to tissue disorder. The above-mentioned systemic lupus erythematosus (SLE) is a typical systemic autoimmune disease that shows immune abnormality such as expression of various autoimmune and the like, and expresses multiple organ failures. Genetic factors and dysfunction of T cells and B cells that cause generation of various autoantibodies including mainly anti-double stranded DNA antibody (anti-ds DNA antibody) have been pointed out as the cause of the disease. Actual clinical symptoms are various, being systemic such as mucocutaneous symptoms, arthritis, pleurisy/pericarditis, neuropsychiatric disorder and the like, and particularly, glomerulonephritis is an important lesion which determines life prognosis.
Conventionally, MRL/lpr mice have been known as typical mouse model of systemic lupus erythematosus (Murphy E D, Roth J B: Autoimmunity and lymphoproliferation: Induction by mutant gene lpr, and acceleration by a male-associated factor in strain BXSB mouse. Genetic Control of Autoimmune Disease (eds. Rose N, Bigazzi P, Warner N), Elsevier North Holland, N.Y., 1978, p 207-221), the MRL/lpr mice are inbred mice by crossing AKR/J, C57BL/6J, C3H/Di, and LG/J, that develops spontaneously arthritis and glomerulonephritis. It has been acknowledged that Lpr gene is an autosomal recessive mutant gene causing proliferation of lymphocytes, which is a mutant of Fas antigen gene inducing apoptosis, and that MRL/lpr mice are deficient type of Fas antigen gene (Watanabe-Fukunaga R, Brannan C I, Copeland N G, Jelkins N A, Nagata S: Lymphoproliferation disorder in mice explained by defects in Fas antigen that mediates apoptosis. Nature 356:314-317, 1992; Takahashi, T., Tanaka, M., Brannan, C. I., Jenkins, N. A., Copeland, N. G., Suda, T., and Nagata, S. (1994). Generalized lymphoproliferative disease in mice, caused by a point mutation in the Fas ligand. Cell 76, 969-976). Although abnormal proliferation of T cells and B cells/overgeneration of immunoglobulin and their detailed mechanism are unknown, it has been reported that generation of various autoantibodies (anti-DNA antibody, anti-Sm antibody and the like) can be induced in the same manner as human diseases (Izui S, Eisenberg R A: Circulating anti-DNA-rheumatoid factor complex in MRL/l mice. Clin Immunol Immunopathological 15:436-551, 1980; Gyotoku Y, Abdelmoula M, Spertini F, Izui S, Lambert P-H: Crioglobulinemia induced by monoclonal immunoglobulin G rheumatoid factors derived from autoimmune MRL/Mpj-lpr/lpr mice. J Immunol 138:3785-3792, 1987). Further, MRL/lpr mice are mice wherein different haplotypes are mixed as mentioned above, and it is known that if they are backcrossed into mice of a strain that develops spontaneously autoimmune abnormality (C3H/HeJ, C57BL/6, AKR), diseases such as arthritis and nephritis are not developed, although autoantibody generation can be observed (Theofilopoulos, A. N., and F. J. Dixon: Murine models of systemic lupus erythematosus. Adv. Immunol. 37:269-390, 1985). Therefore their genetic background is considered to be closely related to the autoimmune pathology of MRL/lpr. On the other hand, Japanese Laid-Open Patent Application No. 9-172908 discloses non-human transgenic vertebrate of systemic lupus erythematosus wherein exogenous genetic structure including IL-1 α gene is incorporated.
The object of the present invention is to provide a non-human animal model of systemic lupus erythematosus wherein generation of anti-double stranded DNA antibody and anti-single stranded DNA antibody is induced, and that develops spontaneously arthritis and glomerulonephritis; and a screening method for a therapeutic agent for systemic lupus erythematosus using said non-human animal model of systemic lupus erythematosus.
The present inventors made a keen study to solve the above problem, and they backcrossed for 12 generations FcγRIIB deficient mouse that does not develop spontaneously autoimmune pathology although its various antibody responses are enhanced, wherein genetic function of FcγRIIB which is inhibitory FcR is deficient on its chromosome, into C57BL/6J (B6) mouse which is a haplotype H-2b to generate FcγRIIB deficient B6 mouse, intercrossed the FcγRIIB deficient B6 male mouse with an Lpr/B6 female mouse to generate FcγRIIB+/−/lpr+/− mouse wherein the both genes are heterozygous; they further crossed the FcγRIIB+/−/lpr+/− mice to generate FcγRIIB deficient lpr/B6 mouse (FcγRIIB−/−/lpr+/+=FcγRIIB−/−/lpr). The above-mentioned FcγRIIB deficient B6 mice are short-lived compared to wild-type mice, wherein notable lymphocytes proliferation is observed, and anti-DNA antibody titer is significantly high. Moreover, glomerulonephritis is developed spontaneously 100% by 16-week-old, and arthritis is developed spontaneously 100% by 24-week-old, thus the present inventors found that by introducing FcγRIIB deficient gene into Lpr/B6 mouse, the mouse develops severe systemic lupus erythematosus. Thus the present invention has been completed.